Version 1.x

Features

Serial console

However, as with other TP-Link models, a little hardware mod is required in most circumstances to get the serial console working properly. Without this mod, you might see garbled chars when using a Prolific PL2302-based level shifter. This is because TP-Link employed some sort of voltage divider as has been reported for the TL-WR741ND as well: RX will have a high level of only 1,7V, whereas the CPU pin itself has the usual 2,5V.

To fix this, you must remove the 2x 5k6 resistors R249 (→ 3.3V) and R251 (→ GND) as well as the capacitor C278. You might want to replace it with a 1K resistor to protect the CPU pin, otherwise bridging the pads will do the job but offers the risk of damaging the CPU port.

After this, the console will be accessible at 115200bps 8N1. Type "tpl" to escape automatic boot and reach U-boot's prompt. Note this is a crippled U-boot: you can not modify the environment settings permanently which is why OpenWrt kernels ignore the kernel command line.

Comment: The WR741ND had the same serial connection, and I fixed it without altering the board, by simply placing a 10k pullup resistor between the TX and 3.3V pins.

Serial console

It's 115200 8N1, software flow control. It's a TTL serial port, so don't plug it directly into a RS232 port. You have to build a TTL-RS232 adaptor to attach your WA901ND to your computer:

With that, you can now use a null modem cable to attach it to your PCs COM port.

To access the boot menu, type "tpl" (without quotes) when you see "autobooting in 1 seconds".

The ethernet port is not enabled in the boot loader. Because of that, TFTP cannot be used to transfer the firmware.

Installation

The default image for this device (tested with v2) has no LuCI at all and no room to install it. So, no web config nor web revert. Be advised! The version OpenWrt Chaos Calmer 15.05 LuCI (git-15.248.30277-3836b45) seems to work and seems to have a working LuCI, your mileage may vary

via Web Interface

You can install OpenWrt via the TP-Link web interface, select the firmware upgrade and browse to your local copy of the pre-compiled binary images below.

Version 4.x

Features

Serial Console

Two tiny resistors (R162, R164) that connect the serial console pads towards the CPU are not placed, you need to solder two tiny bridges for the serial to work from the pads! See the detail picture below. It is possible that these were intended as voltage dividers, but R0 bridges Worked For Us™. Hint: solder the bridges before soldering pins onto the pads.

115200 8N1, software flow control, TTL levels.

The serial console pin order is identical to v3:

3V3 (do not connect)

GND (plug your TTL UART's "GND" cable here)

RX (plug your TTL UART's "TX" cable here, so the UART's Transmit line is connected to the TP-Link's Receive line)

TX (plug your TTL UART's "RX" cable here)

…where TX is the square pad, closest to the front side with the LEDs, as seen in this picture:

Features

Serial Console

Same as in v4 but different, two tiny resistors (R162, R164) that connect the serial console pads towards the CPU are not placed, you need to solder two tiny bridges for the serial to work from the pads! See the detail picture below.

115200 8N1, software flow control, TTL levels.

The serial console pin order, as seen in the picture below:

TX (plug your TTL UART's "RX" cable here)

RX (plug your TTL UART's "TX" cable here, so the UART's Transmit line is connected to the TP-Link's Receive line)